1. Field of the Invention
The present invention relates to a method and apparatus for cleaning a substrate for an electrophotographic photosensitive member and a method of producing an electrophotographic photosensitive member having a functional film formed therein.
2. Related Background Art
As the material of a substrate for forming a deposited film of an electrophotographic photosensitive member thereon, there have been proposed glass, heat-resistant synthetic resin, stainless steel, aluminum, and so on. In practice, however, metals are frequently used in order to stand the electrophotographic process including steps of charging, exposure, development, image transfer, and cleaning and to keep positional accuracy always high enough to prevent degradation of quality of image. Of the metals, aluminum is one of the most suitable materials as a substrate of the electrophotographic photosensitive member because of its good workability, low cost, and light weight.
Techniques concerning the material for the substrate of the electrophotographic photosensitive member are described in Japanese Patent Application Laid-Open Nos. 59-193463 and 60-262936. Japanese Patent Application Laid-Open No. 59-193463 discloses the technology for obtaining an amorphous silicon electrophotographic photosensitive member to implement good quality of image, by employing a support of an aluminum alloy containing Fe in the content of not more than 2000 ppm. Further, this application also discloses procedures for cutting a cylindrical (cylinder-shape) substrate by a lathe, mirror-finishing the surface thereof, and thereafter forming amorphous silicon thereon by a glow discharge.
Japanese Patent Application Laid-Open No. 60-262936 discloses an extruded aluminum alloy excellent in evaporativity of amorphous silicon thereon, the extruded aluminum alloy containing Mg of 3.0 to 6.0 wt %, impurities of Mn not more than 0.3% by weight, Cr less than 0.01% by weight, Fe not more than 0.15% by weight, and Si not-more than 0.12% by weight, and Al the rest.
These materials are subjected to surface processing for the substrate according to use of the electrophotographic photosensitive member and a light receiving layer is formed on the surface. Techniques concerning the surface processing of the substrate are described in Japanese Patent Application Laid-Open Nos. 61-231561 and 62-95545. As corrosion inhibiting technology in a water cleaning step where an aluminum alloy Is used as a substrate, Japanese Patent Application Laid-Open No. 6-273955 suggests the technology for cleaning the substrate with water containing dissolved carbon dioxide, but fails to describe carrying out cleaning such that those surfaces of liquid ejected from nozzles which are in contact with the surface of a cylindrical substrate do not interfere with each other.
Japanese Patent Application Laid-Open No. 3-205824 discloses the technology for clearing comprising jetting high-pressure liquid, but fails to describe carrying out cleaning such that those surfaces of liquid ejected from nozzles which are in contact with the surface of a cylindrical substrate do not interfere with each other.
As the technique for device materials used in the electrophotographic photosensitive member, there have been proposed a variety of materials including selenium, cadmium sulfide, zinc oxide, amorphous silicon, organic material such as phthalocyanine, and so on. Among them, non-monocrystalline deposited films containing the principal component of silicon atoms, typified by amorphous silicon, for example, amorphous deposited films such as amorphous silicon compensated by hydrogen and (/or) halogen (for example, fluorine, chlorine, etc.) or the like, are proposed as high-performance, high-durability, and nonpolluting photosensitive members, and some of them are practically used. Japanese Patent Application Laid-Open No. 54-86341 discloses the technology of the electrophotographic photosensitive member in which the photoconductive layer is formed mainly of amorphous silicon.
As the method of forming such a non-monocrystalline deposited film containing the principal component of silicon atoms, there have hitherto been known many methods such as sputtering, a method of decomposing a source gas by heat (thermal CVD method), a method of decomposing a source gas by light (photo CVD method), a method of decomposing a source gas by plasma (plasma CVD method), and so on.
The plasma CVD method, which is a method of decomposing a source gas by direct current, high frequency wave, or microwave glow discharge or the like to form a thin deposited film on a substrate, is most suitable for formation of the amorphous silicon deposited film for electrophotography and practical use thereof is now well in progress. Among others, the plasma CVD method using decomposition by microwave glow discharge as the deposited film forming method, i.e., the microwave plasma CVD method is drawing attention industrially in recent years.
The microwave plasma CVD method has advantages of high deposition rate and high source gas utilization efficiency as compared with the other methods. An example of the microwave plasma CVD technology making use of such advantages is described in U.S. Pat. No. 4,504,518. The technology described in the patent is one for obtaining a deposited film with high quality at a high deposition rate under the low pressure of not more than 0.1 Torr by the microwave plasma CVD method.
Further, the technology for improving the utilization efficiency of a source gas by the microwave plasma CVD method is described in Japanese Patent Application Laid-Open No. 60-186849. The technology described in the Lead-Open gazette can be summarized as technology for achieving very high source gas utilization efficiency by the arrangement in which substrates are disposed so as to surround a means for introducing a microwave energy to form an internal chamber (i.e., a discharge space).
Moreover, Japanese Patent Application Laid-Open No. 61-283116 discloses improved microwave technology for production of a semiconductor member. Specifically, the Laid-Open gazette discloses the technology for improving characteristics of a deposited film by providing an electrode (bias electrode) for control of the plasma potential in a discharge space, applying a desired voltage (bias voltage) to this bias electrode, and thereby carrying out film deposition while controlling ion bombardment against the deposited film.
When a cylinder of an aluminum alloy is used as a substrate, the method of producing the electrophotographic photosensitive member according to these conventional techniques is carried out specifically as follows.
The substrate Is machined to a flatness of surface within a predetermined range by cutting with a diamond cutting tool set in a lathe, a milling machine, or the like as occasion demands, and then is cleaned with trichloroethane. After this surface processing, the substrate is then cleaned with trichloroethane and a deposited film the matrix of which is amorphous silicon is formed on the substrate.
Further, in the electrophotographic photosensitive members according to the conventional technologies there were many abnormally grown portions, i.e., portions of small area where surface charge was not carried, in the deposited film. These abnormally grown portions appeared particularly prominent in the electrophotographic photosensitive members having the deposited film formed by the plasma CVD method, particularly, like amorphous silicon. Thus, it was conventional practice to decrease the number of those portions where the surface charge was not carried, by optimizing the surface processing conditions of substrates, cleaning conditions, and deposition conditions. Further, the higher resolution in development was not demanded heretofore than at present, go that such portions posed no practical problem before.
However, in recent years, such small portions where charge was not carried have been pointed out as image defects, under the following circumstances: (1) high quality of image was demanded for the electrophotographic apparatus and the resolution in development was being increased therewith, and (2) progress in increase of the copying speed of copying machines made charging conditions severer and the portions carrying no charge in the surface came to greatly affect the potentials around them substantially.
Further, conventional uses of copies were mainly copies of originals including only letters (so-called line copies), so that these image defects were not so prominent in practical use.
However, with increase of copies of originals including halftones such as photographs in recent years, further improvement has been demanded in the quality of image of the copying machines. Particularly, further improvement in the quality of image is desired in color copying machines having popularly been used recently
Incidentally, since the abnormally grown portions are very small, it is very difficult to detect them even by measurement of electric conductivity by an electrode placed thereon. Further, when the charging, exposure, and development steps are carried out in the electrophotographic process on the electrophotographic photosensitive member, particularly, when a uniform image is formed in halftone, a small potential difference on the surface of the electrophotographic photosensitive member appears visually outstanding as an image defect. Particularly, in the electrophotographic photosensitive member made by the microwave plasma CVD method, the aforementioned issue appears further prominent.
In addition, such image defects appear particularly prominent in the electrophotographic photosensitive members made by the plasma CVD method, as compared with the Se electrophotographic photosensitive members made by vacuum evaporation and the OPC electrophotographic photosensitive members made by the blade coating method or the dipping method or the like. In contrast with it, in the case of devices prepared in the similar fashion to the electrophotographic photosensitive members by the plasma CVD method, the overall performance of the devices will not be affected even if there are small differences of electric characteristics among positions on the substrate of the devices; or, in the case of devices that can be corrected by a post-treatment after the preparation by the CVD method, the aforementioned issue will not arise An example of the devices referred to herein is a solar cell.
Moreover, in the conventional techniques trichloroethane was used for cleaning the substrate. However, such chlorine base solvents are not allowed to use without care because of the recent environmental issues, and water bass cleaning has been used instead. However, when aluminum was cleaned with water, cleaning irregularities were not perfectly eliminated by simply ejecting a cleaning fluid under a high pressure. In addition, portions having many impurities (Si etc.) exposed in part in the surface of aluminum sometimes formed local batteries with normal aluminum portions around them, thereby promoting corrosion of the surface of the substrate.